Abstract

Several quantum-mechanics-based descriptors were derived for a diverse set of48 organic compounds using AM1, PM3, HF/6-31 G, and DFT-B3LYP/6-31 G (d) level ofthe theory. LC50 values of acute toxicity of the compounds were correlated to the fatheadminnow and predicted using calculated descriptors by employing ComprehensiveDescriptors for Structural and Statistical Analysis (CODESSA) program. The heuristicmethod, implemented in the CODESSA program for selecting the ‘best’ regression model,was applied to a pre-selection of the most-representative descriptors by sequentiallyeliminating descriptors that did not satisfy a certain level of statistical criterion. First model,statistically, the most significant one has been drawn up with the help of DFT calculationsin which the squared correlation coefficient R2 is 0.85, and the squared cross-validationcorrelation coefficient 2CV R is 0.79. Second model, which has been drawn up with the helpof HF calculations, has its statistical quality very close to the DFT-based one and in thismodel value of R2 is 0.84 and that of R2CV is 0.78. Third and fourth models have been drawnup with the help of AM1 and PM3 calculations, respectively. The values of R2 and R2CV in thethird case are correspondingly 0.79 and 0.66, whereas in the fourth case they are 0.78 and0.65 respectively. Results of this study clearly demonstrate that for the calculations of descriptors in modeling of acute toxicity of organic compounds to the fathead minnow, firstprincipal methods are much more useful than semi-empirical methods.Keywords: Comparative QSTR; fathead minnow; acute toxicity; DFT; HF;

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